tell vim to add default extention to word under my cursor before opening file

Question

Lets say I have text This is result file output_20DeC. Let's say my cursor is on o. When I use the command gf, it should open output_20Dec.txt file.

So how do I tell vim to add a default extension to the word under my cursor before opening file?

Answer 1

To quote the help:

                            *gf* *E446* *E447*
[count]gf       Edit the file whose name is under or after the cursor.
            Mnemonic: "goto file".
            Uses the 'isfname' option to find out which characters
            are supposed to be in a file name.  Trailing
            punctuation characters ".,:;!" are ignored. Escaped
            spaces "\ " are reduced to a single space.
            Uses the 'path' option as a list of directory names to
            look for the file.  See the 'path' option for details
            about relative directories and wildcards.
            Uses the 'suffixesadd' option to check for file names
            with a suffix added.

The key there is the section on 'suffixesadd'; setting to include .txt should do the trick.